1. Field of the Invention
The present invention relates to a water soluble polymer, and more particularly to a photoresist composition containing the water soluble polymer.
2. Description of the Prior Art
In recent years, technology of integrated circuits has progressed quite a lot, and photoresists have long been used for the preparation of printed circuit boards and solder masks. The resins used in the photoresist are mainly organic solvent soluble resins, and the photoresist is developed with organic solvents to form circuits. The conventional phohotoresist used for printed circuit boards contains about 40-70 wt % of organic solvent. During the exposing and developing process, about 60-80% of the organic solvent will evaporate into the air, which is detrimental to human health and environment. For the environmental concern, aqueous alkaline solutions has been developed as the developing reagent.
To further lessen the volatile organic compounds (VOCs) problem, some water soluble photoresists have been developed, such as acrylate latexes and water soluble epoxy resins. The water soluble photoresist can not only be dissolved in water, but also has the advantage of easier handling.
In U.S. Pat. No. 5,411,837, the waterborne photoresist is prepared by emulsion polymerization. A surfactant should be added to maintain the dispersion stability of latex. However, the surfactant easily pollutes the developing tank and affects the adhesion of the photoresist with copper. In U.S. Pat. No. 5,045,435, an alkaline reagent (such as ammonia) is used to partially neutralize a carboxyl group-containing acrylic copolymer which is water insoluble so as to convert it into a water soluble latex. However, the water soluble latex has low photosensitivity.
The object of the present invention is to solve the above-mentioned problems and to provide a water soluble polymer having high photosensitivity, good water dispersability, and storage stability.
Another object of the present invention is to provide a photoresist composition. When the photoresist composition is coated on a printed circuit board, then dried and exposed to UV light afterwards, it is not tacky and will not stick to the mask. In addition, it has good adhesion to the copper on the printed circuit board.
To achieve the above-mentioned objects, the water soluble polymer of the present invention is prepared by the following steps of:
(a) reacting a carboxyl group-containing polymer with an alkaline reagent so that a portion of the carboxyl groups are reacted in an amount sufficient to make the polymer water soluble; and
(b) reacting the polymer obtained from step (a) with an unsaturated bonds-containing epoxide and/or heteroatoms-containing epoxide so that 1 to 100 mole percent of the remaining carboxyl groups of the polymer are reacted with the epoxide to form ester groups via a ring-opening reaction of epoxides, wherein the heteroatom is selected from the group consisting of silicon, nitrogen, phosphorous, and sulfur.
The photoresist composition of the present invention includes the following components:
(1) 10 to 50 weight % of a photosensitive resin which is a water soluble polymer prepared by the following steps of:
(a) reacting a carboxyl group-containing polymer with an alkaline reagent so that a portion of the carboxyl groups are reacted in an amount sufficient to make the polymer water soluble; and
(b) reacting the polymer obtained from step (a) with an unsaturated bonds-containing epoxide and/or heteroatoms-containing epoxide so that 1 to 100 mole percent of the remaining carboxyl groups of the polymer are reacted with the epoxide to form ester groups via a ring-opening reaction of epoxides, wherein the heteroatom is selected from the group consisting of silicon, nitrogen, phosphorous, and sulfur;
(2) 0.1 to 10 weight % of a photoinitiator;
(3) 5 to 50 weight % of a photopolymerizable reactive monomer; and
(4) 30 to 75 weight % of water.
According to the present invention, the water soluble polymer is prepared by the following steps. First, a water insoluble carboxyl group-containing polymer is reacted with an alkaline reagent so that a portion of the carboxyl groups are reacted in an amount sufficient to make the polymer water soluble. Then, the obtained polymer is reacted with an unsaturated bonds-containing epoxide and/or heteroatoms-containing epoxide to form ester groups via a ring-opening reaction of epoxides. In this manner, side chains containing unsaturated bonds and/or side chains containing heteroatoms can thus be introduced into the polymer. Thus, the water soluble polymer of the present invention is obtained. By means of the ring-opening reaction of epoxides, 1 to 100 mole percent of the remaining carboxyl groups of the polymer are reacted. Therefore, the final water soluble polymer may or may not have carboxyl groups.
In the situation that unsaturated side chains are introduced into the polymer, when the water soluble polymer of the present invention is exposed to light to undergo photocuring, the high ratio of unsaturated bonds can increase the photosensivity of the polymer. Moreover, the introduction of side chains can also increase the flexibity of the polymer. In addition, in the situation that heteroatom side chains are introduced into the polymer, it may improve the adhesion between the polymer and the copper surface.
According to the present invention, the water insoluble carboxyl group-containing polymer can be a homopolymer or a copolymer of acrylic acids, acrylates, methacrylic acids, methacrylates, anhydrides or mixtures thereof. For example, it can be a copolymer of monomer A and monomer B. The monomer A can be acrylic acids, acrylates, methacrylic acids, methacrylates, anhydrides and mixtures thereof, and the monomer B is a styrene. The anhydrides suitable for use in the present invention include maleic anhydride, methyl maleic anhydride, endo-5-norbornene-2,3-dicarboxylic anhydride, and cis-1,2,3,6-tetrahydrophthalic anhydride.
In the present invention, the purpose of the alkaline reagent is to partially neutralize the carboxyl groups in the water insoluble polymer so as to make the polymer water soluble. The alkaline reagents suitable for use in the present invention include ammonium hydroxide (NH4OH; ammonia water), sodium hydroxide, potassium hydroxide, 4-methylmorpholine, 2-amino-2-methyl-1-propanol, 2-dimethylamino-2-methyl-1-propanol, monoethanol amine, N,N-dimethylethanolamine, methyldiethanol amine, and morpholine.
According to the present invention, after the water insoluble carboxyl group-containing polymer is treated with the alkaline reagent, the epoxide used to react with the carboxyl groups can be the unsaturated bonds-containing epoxide only or the heteroatoms-containing epoxide only. Also, the unsaturated bonds-containing epoxide and the heteroatoms-containing epoxide can both be used.
The unsaturated bonds-containing epoxide suitable for use in the present invention can be glycidyl acrylate, glycidyl methacrylate, p-epoxy-styrene, p-glycidyl-styrene, or allyl glycidyl ether.
As to the heteroatoms-containing epoxide, the heteroatom refers to silicon, nitrogen, phosphorous, and sulfur. Representative examples include 3-glycidyloxypropyltrimethoxy silane or xcex2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane.
According to the present invention, the ring-opening reaction of the epoxide and the polymer treated with the alkaline reagent is preferably conducted at the presence of a phase transfer catalyst. Representative examples of the phase transfer catalyst suitable for use in the present invention include tetrabutylammonium bromide, tetrapropylammonium bromide, tetramethylammonium bromide, tetrabutylphosphonium bromide, tetraphenylphosphonium bromide, benzyl triethylammonium bromide, ethyl trioctyl phosphonium chloride, methyl trioctyl ammonium chloride, tetraphenylphosphonium chloride, methyl triphenylphosphonium chloride, tetrabutylammonium chloride, tetrabutylammonium iodide, and tetraphenylphosphonium iodide.
Preferably, the water soluble polymer of the present invention has a molecular weight of 5000 to 250000 and an acid value of 50 to 250.
The water soluble side chain-containing polymer of the present invention can be used as a photosensitive resin. A water soluble photoresist composition can be obtained by dissolving 10 to 50 weight % of the water soluble polymer of the present invention, 0.1 to 10 weight % of a photoinitiator, and 5 to 50 weight % of a photopolymerizable reactive monomer in 30 to 75 weight % of water. (The total weight of the photoresist composition is 100 weight %.) Preferably, the photoresist composition includes 15 to 35 weight % of the water soluble polymer of the present invention, 3 to 7 weight % of a photoinitiator, 15 to 35 weight % of a photopolymerizable reactive monomer, and 40 to 60 weight % of water.
The photoresist composition of the present invention is a negative type. That is, when the photoresist composition of the present invention is exposed to UV light, the exposed portion will undergo photocuring reaction, and the unexposed portion can be dissolved in a weak alkaline solution. The photoresist composition has high photosensitivity, good water dispersability, and storage stability. When the photoresist composition is coated on a printed circuit board, then dried and exposed to UV light, it is not tacky and will not stick to the mask. In addition, it has good adhesion to the copper on the printed circuit board.
The photoinitiator suitable for use in the present invention can be benzoin, benzoin alkyl ether, benzil, ketals, acetophenones, benzophenone, 4,4xe2x80x2-dimethyl-amino-benzophenone, thioxanthones, or morpholino-propanones.
The photopolymerizable reactive monomer suitable for use in the present invention can be a multifunctional acrylate or methacrylate. Representative examples include tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, neopentylglycol diacrylate, neopentylglycol dimethyl acrylate, polyethylene glycol diacrylate, polyethylene glycol dimethylacrylate, ethoxylated bisphenol A glycol diacrylate, ethoxylated bisphenol A glycol dimethyl acrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, glyceryl propoxy triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol pentaacrylate.
The following examples are intended to illustrate the process and the advantages of the present invention more fully without limiting its scope, since numerous modifications and variations will be apparent to those skilled in the art.